The present invention relates to a grooved refractory component and more particularly to a refractory pouring tube for metallurgical casting, and assembly of refractory components, a casting installation and a process for repairing the contact face of a refractory component.
It is known that the casting of steel calls for the filling of successive metallurgical vessels, notably a ladle, a tundish and ingot moulds, and that during its passage from one upper metallurgical vessel to a lower metallurgical vessel, the metal must as far as possible be kept out of all contact with the ambient air.
To this end, a pouring shroud or a submerged entry nozzle made of refractory material forms an extension to the pouring orifice of the upper vessel (respectively the ladle or tundish), and enters the molten metal present in the lower vessel (respectively the tundish or ingot mould), so that the molten metal passes from the ladle to the tundish or from the tundish to the ingot mould without ever being exposed to the ambient air.
The pouring orifice of the upper vessel incorporates an inner nozzle in refractory material, which opens below this vessel via a contact surface designed to mate with a contact surface on the pouring shroud or submerged entry nozzle, thereby forming a joint face between these two components.
Conventionally, a casting installation also includes means of regulating the flow of the molten metal. These means may consist of a stopper rod which enters the metal bath of the upper vessel opposite the pouring orifice and whose degree of immersion in the said metal bath determines the opening of the said pouring orifice. Alternatively, use may also be made of a slide valve incorporating a set of refractory plates each having an orifice. These plates are normally located between the inner nozzle and the pouring shroud or the submerged entry nozzle. The degree of alignment of the orifices in adjacent plates determines the flow of molten metal.
A continuous casting installation therefore includes numerous assembled refractory components, the interfaces between which are formed by contact surfaces that may be planar or non-planar, as indicated for example in document U.S. Pat. No. 5,984,153.
It is known that the reductions in cross-section which occur along the molten metal pouring channel produce considerable negative pressure which can in turn lead to an induction of air.
The joint surface is generally effective in avoiding air induction problems, but it has been found that it has a tendency to deteriorate at each replacement of the pouring shroud or submerged entry nozzle.
This replacement can be carried out, in a known manner, by positioning a new tube beside the tube to be replaced, then simultaneously moving the two tubes, allowing the new tube to displace the old one and take its place beneath the inner nozzle.
Prior to each replacement, the tundish pouring orifice is closed off, but it is possible for droplets of molten metal to remain at the joint surface, at the interface between the pouring orifices of the tube and the inner nozzle. These droplets, which solidify, are drawn into the joint surface and cause more or less severe damage to the contact face of the inner nozzle. As it is not possible to replace the inner nozzle during casting, it is essential to preserve the integrity of this nozzle and in particular its lower contact face, so that the sealing tightness of the joint surface formed with the contact face of the tube is maintained for as long as possible and so that, consequently, the casting operation need not be prematurely interrupted.
This problem is further exacerbated if the joint surface incorporates an injection channel for a fluid, such as an inert gas, which may have the function both of preventing the ingress of ambient into the joint surface and/or allowing the injection of a sealing agent into the joint surface (as shown in documents WO 98/17420 and WO 98/17421, in order to treat the cracks which invariably propagate on the contact face of the inner nozzle and the score marks or scratches produced during tube changes.
The droplets of metal trapped at the joint surface accumulate in the injection channel and can cause it to become obstructed, thereby rendering it ineffective both in terms of preventing the admission of ambient air and in terms of the treatment of cracks and score marks or scratches.
When the tube is moved for the purposes of replacement, the extraneous material obstructing the injection channel is sheared between the two contact faces and spreads notably over part of the contact face of the inner nozzle.
The aim of the present invention is to remedy these problems in a simple and economic manner.
The object of the present invention is a refractory pouring tube forming part of a pouring channel and including at least one contact face capable of bearing against a contact face of another refractory component forming an adjacent portion of the pouring channel, the said pouring tube being arranged to be displaced in a predefined trajectory along which its contact face slides and remains in bearing contact against the contact face of the other refractory component, the said pouring tube being characterised in that its contact face incorporates a cleaning groove delineated notably by a wall presenting an edge capable of exerting a scraping action, as the said pouring tube is displaced, at least partially on the determinate part of the contact face of the other refractory component.
The pouring tube which is the object of the invention can be for example a submerged entry nozzle or pouring shroud.
It is to be understood that, as it passes over the contact face of the other refractory component, the cleaning groove picks up all of the extraneous material accumulated on the latter, and notably any metal droplets entrained during the relative movement of the two refractory components.
Thus, for a refractory pouring tube whose replacement is effected by simultaneous movement of the said pouring tube and its replacement pouring tube which displaces the former and takes its place in the working position, the cleaning groove is found to be highly effective in clearing the joint surface of all dirt and extraneous matter such as metal droplets entrained during the movement of the two refractory components. Depending on whether the cleaning groove is located ahead of or behind the pouring channel in relation to the direction of movement of the two components, the refractory pouring tube performs the scraping action for itself when it replaces a previous refractory pouring tube, or for a succeeding refractory pouring tube when the said refractory pouring tube is replaced by the next refractory pouring tube.
In a preferred embodiment of the invention, the cleaning groove is positioned so that the cleaning edge is able to scrape the entirety of the determinate part of the contact face of the other refractory component.
One possibility to achieve this purpose is for the cleaning groove to be located behind the pouring channel in relation to the direction of movement of the refractory pouring tube, so that it passes over the determinate part of the contact face from its border with the pouring orifice up to its edge. In this case, the cleaning groove exerts its action not for the refractory pouring tube in which it is incorporated, but for its replacement.
According to a particular characteristic of the invention, the cleaning groove is blind. Preferably, the cleaning groove should have a width such that, when the groove is at the level of the pouring orifice (for example when the tube is changed), it does not communicate with the injection groove. Thus, if some molten metal remains at the interface between the pouring orifices of the inner nozzle and the submerged entry nozzle, it will not reach the injection groove. Therefore, according to an advantageous characteristic of the invention, the cleaning groove is shorter than the minimum width between opposite sections of the injection groove on either side of the pouring orifice at the level of the pouring orifice.
In a particular embodiment of the invention, the contact face of the refractory pouring tube incorporates a second groove essentially parallel to the cleaning groove.
This second groove may be located, relative to the first groove, on the other side of the pouring channel. It may even be symmetrical with the cleaning groove relative to the pouring channel, which is particularly advantageous if the refractory pouring tube can be used in two possible positions, by virtue of its own axial symmetry, as is the case with certain pouring shrouds or submerged entry nozzles.
In a particular embodiment of the invention, the second groove partially covers an injection groove in the other refractory component defining an injection channel.
The second groove then performs a different function from the cleaning groove, namely that it allows a fluid injected into the injection channel to bypass a part of the said channel which may be blocked.
In order to avoid obstruction of the inlet or outlet of the injection channel, notably by a sealing agent carried by the injected fluid, the second groove may be formed so as to cover the opening of a delivery line and, where appropriate, discharge line of the fluid injection channel.
In a particular embodiment of the invention, the refractory pouring tube incorporates several grooves capable of scraping at least partially the determinate part of the contact face of the other refractory component.
The object of the present invention is also an assembly of refractory components forming a pouring channel and each incorporating at least one contact face bearing against the contact face of another adjacent refractory component, characterised in that one of the refractory components is a refractory pouring tube as described above.
In a particular embodiment of this assembly, the other refractory component incorporates an injection groove which forms an injection channel with the contact face of the refractory pouring tube incorporating the cleaning groove, into which injection channel emerges a delivery line and, where appropriate, discharge line provided in one or more of the refractory components.
The object of the present invention is also a casting installation including an upper metallurgical vessel and a lower metallurgical vessel connected by a pouring channel defined notably by an assembly of refractory components as described above.
According to a particular characteristic, the assembly of refractory components is equipped with an injection channel and the casting installation includes a fluid source connected to the delivery line of the fluid injection channel.
According to an additional characteristic, the casting installation also includes a means of injecting a sealing agent, for example powdered graphite, into the fluid.
A further object of the present invention is a process for repairing the contact face of a refractory component forming part of a pouring channel, the said contact face being capable of serving as a bearing surface for a contact face of another refractory component (i.e. a pouring tube) forming an adjacent part of the pouring channel, the said other component being arranged to be displaced in a pre-defined trajectory along which its contact face slides and remains in bearing contact against the contact face to be repaired, whilst the portion of the pouring channel formed by the said other component defines a determinate part of the contact face to be repaired, the process being characterised in that, as the pouring tube is displaced, the determinate part of the contact face to be repaired is scraped at least partially by the cleaning groove formed on the contact face of the said pouring tube and delineated notably by a wall presenting an edge suitably shaped for this purpose.
In order to better explain the invention, a mode of implementation given by way of example which does not limit the scope of the invention will be described below with reference to the attached diagram in which: